The present invention relates to ring assemblies and ring assembly manufacturing methods and apparatus that employ the use of infrared energy.
Ring assemblies are commonly used as gears, for example, within electronic power steering systems. These ring assemblies may be xe2x80x9cblankxe2x80x9d in nature, where the blank is machined into a gear via subsequent processing. Alternately gear tooth geometry may be pre-existing in the ring and this process joins a gear ring to a structural hub. These gears can be various styles, for example, worm gears, spur gears, or face gears. Furthermore, ring assemblies are employed aside from gears, for example, in cam lobes, spacers, washers, flywheels or bushings. Ring assemblies are typically circular in shape; however, other shapes, including elliptical, oval, or triangular are commonly employed in various applications.
Certain ring assemblies include a ring of polymeric material having a central metal hub. Conventional manufacturing of such polymer ring/central metal hub assemblies is accomplished by securing the polymer ring over the metal hub, by, for example, traditional fastening means such as rivets or screws. Other techniques take advantage of the thermal expansion properties of the polymer ring. A polymer ring is placed in a heating device such as a furnace until the central opening has expanded sufficiently to be pressed fitted over a hub which has mechanical interlocking features on its perimeter (e.g., knurl or splines). Subsequent contraction of the polymer facilitates a reliable union between the ring and hub.
In an operation employing the latter method, typically, one or more rings are placed in a furnace chamber and heated by convection and radiation for about 1-1.75 hours. This amount of time is generally required to achieve a heat soak time of approximately 7-8 minutes. A xe2x80x9cheat soakxe2x80x9d occurs when the heat has diffused from the surface to saturate the body of the rings. After the rings have heated to achieve the required expansion, they are removed from the furnace and pressed over hubs. The gear assembly then is allowed to cool whereupon the ring shrinks and is affixed to the hub. The hubs can include features such as knurls, splines, or grooves where the molten material can adhere to hub providing robust attachment in both radial and transverse directions. The cooling time depends generally on the dimensions of the ring, as the entire ring is heated to temperature to achieve expansion. The manufacturing may also be accomplished using billets and tubes which are subsequently cut to dimension (e.g., by computer numerical control, or CNC, techniques).
Another process that may be employed to further adhere the polymer ring to the metal hub involves heat induction of the polymer ring/metal hub assembly. The hub having die ring press fitted thereon is placed inside an induction coil and an alternating current is introduced. The current causes the metal hub to heat, whereby the heated metal melts the polymer surface adjacent to it. The molten polymer flows into mechanical interlocking features on hub allowing for a strong bond between the metal hub and the polymer ring.
The conventional heating methods (i.e., radiation and convection) dictate the time required to heat the polymer ring to cause expansion sufficient to allow the polymer ring to be press fit over the metal hub. A method of manufacturing gear assemblies and a suitable apparatus that is capable of producing ring assemblies in less time and with fewer process steps is desirable.
The instant invention provides a method and apparatus for forming assemblies having a plurality of layers wherein one layer is fused or adhered to another layer. An apparatus is employed having one or more infrared sources therein to heat a ring, generally a polymeric ring, for expansion and of surface melting.
The infrared heating provides rapid, concentrated and selective energy to a region of the ring exposed to the energy. Where the inside diameter surface is exposed to the infrared energy, the central opening expands. When expanded, the ring is press fit over an inner ring such as a metallic hub. Upon cooling, the outer ring contracts and a strong bond is effectuated between the inner ring and the outer ring. Features can be provided on the outer edge surface of the hub (or inner ring) to enhance the bond.
The cooling time is relatively short in the process of the invention since the selective heating does not equally affect the entire ring. Therefore, the overall assembly time is decreased compared to conventional heating techniques. Furthermore, a bond is achieved that is uniform since the infrared energy can be directed to the portions of the ring that are to be adhered.
Another apparatus includes one or more infrared sources for heating a polymeric ring at the inside diameter surface and one or more infrared sources for heating the polymeric ring at the outside diameter surface. Both sets of sources allow the ring to expand such that it can be press fit over a metallic hub. This is particularly useful, for example, when more rapid thermal expansion is desired.
In another embodiment of the instant invention, an assembly line is provided having a chamber for expanding the polymeric ring with infrared energy and another device for press fitting the ring over a metallic hub. Alternatively, a lift device is configured to both introduce the ring into the infrared chamber and to the press fining device.